Methods to detect linkage in man are sophisticated. Methods to map linkages (once detected) are primitive. This project is directed to the second problem, the seriousness of which did not become apparent until many linkages were found or claimed. How are genetic, cytological, and cell hybridization studies to be interpreted in the most efficient way? Given lod scores for linkage, cytological markers, chiasma distributions, and step functions from somatic cell hybridization, we propose to develop maximum likelihood linkage maps and tests of hypotheses about mapping functions, linear orders, and homogeneity, to apply these methods to all recognized linkage groups in man, and to make the resultant system readily accessible for updating and analysis.